JP2008093715A - High yield strength and high toughness flux-cored wire for gas-shielded arc welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flux-cored wire for gas-shielded arc welding, which is used for welding a high tension steel plate having tensile strength in the class of ≥950 MPa. <P>SOLUTION: A flux-cored wire for gas-shielded arc welding that has high yield strength and high toughness contains, in a steel-made shell and a flux, as metal or alloy, in terms of total mass% based on the entire mass of the wire, 0.08-0.3% C, 0.2-2% Si, 0.5-2.5% Mn, ≤0.02% P, ≤0.01% S, 0.002-0.3% Al, 0.005-0.3% Ti, 0.5-11% Ni, 0.012-0.5% Mg, and one or more elements of 0.1-4% Mo, 0.1-3% W, 0.005-0.1% Nb, 0.005-0.5% V, and 0.005-0.5% Ta. Further, each of elements that affects hardenability, precipitation strengthening, and deoxidation is controlled by parameters. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention is a welding wire used for gas shielded arc welding of an ultra-high strength steel sheet having a tensile strength TS of about 950 to 1400 MPa applied to applications such as construction machinery and industrial machinery. High strength and high toughness gas with which a weld metal having a thickness TS of 1200 MPa or more, a yield strength YP of 1000 MPa or more, and an absorption energy vE- ₄₀ of 27 J or more in a 2 mm V notch Charpy impact test at −40 ° C. is obtained. The present invention relates to a flux-cored wire for shielded arc welding.

  In recent years, as the demand for larger and lighter structures such as construction machinery and industrial machinery has increased, the steel plates used have been increased in tension, and recently, high tensile strength steels with a tensile strength TS of 780 MPa or higher. It is considered that the use of ultra high strength steel having a tensile strength TS of 950 MPa or more and further a tensile strength TS of 1200 MPa or more will increase in the future.

  Further, as the strength of the steel plate for steel structure, it is required to improve the yield stress YP as well as the tensile strength TS. For a high strength steel plate having a tensile strength TS of 950 MPa or more, the yield stress YP is 850 MPa or more. In the ultra high strength steel having a thickness TS of 1200 MPa or more, it is desired that the yield stress YP is 1100 MPa or more.

  When a steel structure is manufactured by welding such a high-tensile steel plate having a high tensile strength TS and a high yield strength, a welded joint, particularly a weld metal tensile strength TS and Improvement of the yield stress YP is required. In ordinary welded joints, the strength of the weld metal is often higher than that of the base material and is designed to be overmatched. Therefore, the strength of the weld metal needs to be higher than or equal to the tensile strength of the steel plate.

Steel structures are often applied to applications that require high-temperature toughness as well as high strength. When producing a welded joint using a high-strength steel sheet having a tensile strength of 950 MPa or higher, the toughness of the weld metal is lowered, and it becomes difficult to obtain a weld metal with high strength and high toughness. Moreover, in high strength steel plates and weld metals, there is concern about the occurrence of cold cracking due to hydrogen contained in the weld metal. In general, from the viewpoint of cold cracking and toughness of the weld metal, the amount of hydrogen in the weld metal can be reduced, and a weld joint with high strength and toughness can be obtained. MIG welding, MAG welding (Ar + CO ₂ welding or CO ₂ welding), gas shield arc welding such as TIG welding is preferable. Among these, TIG welding is particularly suitable for improving the toughness of the weld metal, but since the welding efficiency is inferior to MIG welding and MAG welding, practically by MIG welding and MAG welding, There is a demand for efficiently producing a high-strength, high-toughness welded joint while suppressing the occurrence of cold cracks in the weld.

  Means for achieving a high-strength, high-toughness welded joint when gas-shielded arc welding is performed on a high-tensile steel plate having a tensile strength of 780 to 900 MPa class has been studied.

For example, when gas shielded arc welding is performed on a thick high-strength steel sheet having a thickness of 50 mm or more and a tensile strength of 900 MPa or more, the tensile strength of the weld metal is 0.95 times or less of the tensile strength of the steel sheet, By setting the surface width and the back surface width of the weld metal in the cross section to less than 0.45 times the plate thickness and the ratio of the square of the cross section of the weld metal to the plate thickness to less than 0.4, the tensile strength TS is A method for obtaining a welded joint excellent in toughness and toughness for forming a weld metal having a tensile strength TS of 988 MPa and a Charpy absorbed energy (vE _-20 ) of 74 J at 20 ° C. with respect to a 1070 MPa steel plate has been proposed. (For example, refer to Patent Document 1). In this method, when welding a high-strength steel sheet having a thickness of 50 mm or more and a tensile strength of 900 MPa or more, the tensile strength of the weld metal is reduced in order to suppress the mixed structure of martensite and bainite, which causes a decrease in toughness. The width and cross-sectional area of the weld metal (weld bead) are restricted from the relationship with the plate thickness in order to lower the tensile strength of the steel plate (undermatching) and ensure the joint strength. However, in this method, since welding conditions are restricted, it is difficult to achieve a welded joint excellent in toughness having a weld metal having a tensile strength TS of 1100 MPa or more, while lowering the welding construction efficiency.

On the other hand, a method for improving the strength and toughness of the weld metal by designing the composition of the welding wire without depending on the restriction of the welding conditions has been studied. For example, C, Si, Mn, P, S, Al, Ti, Ni And Mg are contained in a predetermined amount, and further one or more of Mo, W, Nb, V and Ta are contained in a predetermined amount, and carbon equivalent (Ceq.) And Nb equivalent (Nbeq.) Are predetermined. By controlling within the range, a solid wire is proposed in which a weld metal with a tensile strength TS of 950 to 1500 MPa, a yield stress YS of 900 to 1400 MPa, and a toughness of ₄₀ to 127 J with Charpy absorbed energy vE- ₄₀ can be obtained. (For example, refer to Patent Document 2). This wire contains a relatively large amount of Ni, which has a large effect of maintaining both strength and toughness, and is a precipitating element of one or more of Mo, W, Nb, V, and Ta under conditions that ensure quenching component properties. To precipitate the carbonitride in the weld metal, thereby pinning the movement of the mobile dislocation density in the martensite main structure and suppressing the formation of retained austenite, thereby reducing the tensile strength TS of the weld metal. , Yield stress YS and toughness vE- ₄₀ are both improved.

According to this solid wire, the tensile strength TS, yield stress YS, and toughness vE- ₄₀ of the weld metal can be improved together. However, since the strength of the material used for wire manufacture increases and work hardening at the time of wire drawing is added, the frequency of occurrence of wire breakage in the wire drawing process increases. In addition, it is necessary to perform an annealing process for softening the material. However, since this annealing treatment step causes a reduction in productivity and manufacturing cost during wire production, it is preferable that the softening treatment of the material such as the annealing treatment step can be omitted in order to improve the productivity of wire production.

  In general, flux-cored wire can contain a large amount of metal or alloy in the flux filled in the steel outer sheath without greatly changing the steel material composition of the steel outer sheath. A lot of quenching elements can be contained in the wire without lowering.

  However, when a large amount of quenching elements are contained in the flux of the flux-cored wire in a powder state of metal or alloy, there are the following technical problems specific to the flux-cored wire that are not a problem for the solid wire. That is, when manufacturing a flux-cored wire, a flux blending and granulating step not required for a solid wire is required. At this time, if a large amount of quenching element is mixed in the flux in the powder state of the metal or alloy, the fine powder particle surface of the metal or alloy is oxidized or adsorbed by oxygen molecules or atoms on the metal or alloy powder surface. However, due to these causes, the oxygen content in the wire is likely to increase as compared with the solid wire. In addition, in the flux blending and granulating steps, moisture in the atmosphere is absorbed into the metal or alloy powder, so that the increase in the hydrogen content, which is not a problem with the solid wire, becomes significant.

  The increase in the oxygen content in the flux-cored wire is particularly high in the case of a high strength weld metal in which the yield stress YP of the weld metal is 1000 MPa or more and the tensile strength TS is 1200 MPa or more. Not only does this lead to a decrease in workability and compositional deformability, which are practically problematic, but also increases the possibility of significant deterioration in brittle fracture characteristics in welded joints.

  Further, the increase in the hydrogen content in the flux-cored wire is that the susceptibility to low-temperature cracking is extremely high. When the yield stress YP is 1000 MPa or more and the tensile strength TS is 1200 MPa or more, the diffusibility in the weld metal during welding is increased. The increase in hydrogen causes the cold cracking of the weld metal to occur remarkably.

As described above, a solid that can obtain a weld metal having a tensile strength TS of 950 MPa or more, a yield stress YS of 900 MPa or more, and a good toughness vE- ₄₀ as shown in Patent Document 2 by recent technological development of a high-strength wire. Wire is being realized. However, flux-cored wires have technical problems such as cold cracking of weld metal and reduced toughness and ductility due to the increase in oxygen and hydrogen content in the wire as described above. At present, a flux-cored wire that can exhibit tensile strength TS, yield stress YS, and toughness vE- ₄₀ equal to or higher than that of a conventional solid wire while preventing it has not been realized yet.

JP 2001-1148 A JP 2006-110581 A

In view of the above background art, the present invention provides a solid steel as a gas shielded arc welding wire used for MIG welding, MAG welding (Ar + CO ₂ welding or CO ₂ welding), etc., of a high-tensile steel sheet having a tensile strength TS of 950 MPa class or higher. It is a flux wire with excellent productivity compared to wires, and can achieve a weld metal with a tensile strength of 1200 MPa or more, a yield strength of 1000 MPa or more, and an absorbed energy of 27 J or more in a 2 mmV notch Charpy impact test at -40 ° C. And it aims at providing the flux cored wire which can implement | achieve the low temperature crack-proof property whose cold crack stop temperature in the y-type weld crack test of a weld metal is 150 degrees C or less.

  The present invention solves the above technical problems, and the requirements of the invention are as follows.

(1) In a flux-cored wire in which a flux is filled inside a steel outer sheath,
In the steel outer shell and the flux, as a metal or an alloy, in a total mass% based on the total mass of the wire,
C: 0.08 to 0.3%,
Si: 0.2-2%
Mn: 0.5 to 2.5%
P: 0.02% or less,
S: 0.01% or less,
Al: 0.002 to 0.3%,
Ti: 0.005 to 0.3%,
Ni: 0.5 to 11%,
Mg: 0.012-0.5%,
And a carbon equivalent (Ceq.) Represented by the following formula (1) is 0.7 to 2%, and a deoxidizing element equivalent (Aleq.) Represented by the following formula (2) is 0.2 to 0. 6%, and
Mo: 0.1 to 4%
W: 0.1 to 3%
Nb: 0.005 to 0.1%,
V: 0.005-0.5% and
Ta: 0.005 to 0.5%,
1 or 2 or more of them, and the Nb equivalent (Nbeq.) Represented by the following formula (3) is 0.05 to 0.5%, and the slag contained in the flux The total content of the forming agent and the arc stabilizer is limited to 20% or less by mass% with respect to the total mass of the wire, the balance is Fe and inevitable impurities, and the steel outer shell is a seamless pipe. High yield strength, high toughness, flux-cored wire for gas shielded arc welding.
Ceq. = [C%] + [Mn%] / 6+ [Si%] / 24+ [Ni%] / 40+ [Mo%] / 4+ [W%] / 8 (1)
Aleq. = [Al%] + [Mg%] + [Ti%] / 10% + ([Si%] + [Mn%]) / 30 (2)
Nbeq. = [Nb%] + [V%] / 5+ [Mo%] / 20+ [W%] / 10+ [Ta%] / 5 (3)
However, the above [C%], [Mn%], [Si%], [Ni%], [Mo%], [W%], [Al%], [Mg%], [Ti%], [Nb] %], [V%], and [Ta%] are the contents of C, Mn, Si, Ni, Mo, W, Al, Mg, Ti, Nb, V, and Ta contained in the steel outer sheath and flux in the wire, respectively. The sum of mass% with respect to the total mass of the wire is shown.
(2) In the steel outer shell and flux, as a metal or an alloy, further, in a total of mass% with respect to the total mass of the wire,
Cu: 0.01 to 1.5%,
Cr: 0.01-2%
Co: 0.01-6%, and
B: 0.001 to 0.015%,
1 or 2 or more, and the carbon equivalent (Ceq.) Represented by the following formula (4) is 0.7 to 2%: Yield strength high toughness flux cored wire for gas shielded arc welding.
Ceq. = [C%] + [Mn%] / 6+ [Si%] / 24+ [Ni%] / 40+ [Cr%] / 5+ [Mo%] / 4+ [W%] / 8 (4)
However, the above [C%], [Mn%], [Si%], [Ni%], [Cr%], [Mo%] and [W%] are contained in the steel outer sheath and the flux in the wire, respectively. The total of the mass% with respect to the total mass of the wire of C, Mn, Si, Ni, Cr, Mo, and W is shown.
(3) In mass%,
Ca: 0.0002 to 0.01%, and
REM: 0.0002 to 0.01%
The deoxidizing element equivalent (Aleq.) Represented by the following formula (5) is 0.2 to 0.6%: The flux cored wire for high yield strength and toughness gas shielded arc welding as described in (2).
Aleq. = [Al%] + [Mg%] + [Ca%] + [REM%] / 5+ [Ti%] / 10% + ([Si%] + [Mn%]) / 30 (5)
However, the above [Al%], [Mg%], [Ca%], [REM%], [Ti], [Si], and [Mn] are Al contained in the steel outer sheath and flux in the wire, respectively. The total of the mass% with respect to the wire total mass of Mg, Ca, REM, Ti, Si, and Mn is shown.
(4) The flux-cored wire according to any one of the above (1) to (3) is a heating temperature of 600 to 1100 ° C. after the flux is filled in the steel outer shell, or during or after wire drawing. A flux cored wire for high yield strength, high toughness, gas shielded arc welding, characterized by being annealed with.

According to the present invention, as a wire for gas shielded arc welding used for MIG welding, MAG welding (Ar + CO ₂ welding or CO ₂ welding), etc., in a high-tensile steel sheet having a tensile strength of 950 MPa or more, productivity is higher than that of a solid wire. Weld metal with a tensile strength TS of 1200 MPa or more, a yield strength YP of 1000 MPa or more, and an absorbed energy vE- ₄₀ in a 2 mm V notch Charpy impact test at −40 ° C. of 27 J or more. In addition, it is possible to provide a flux-cored wire that can achieve low-temperature cracking resistance with a low-temperature cracking stop temperature in a y-type weld cracking test of a weld metal of 150 ° C. or lower. large.

Embodiments of the present invention will be described below.
Since the weld metal is basically a solidified structure, it cannot be controlled by the fine graining process such as hot rolling or the tempering process of the entire structure like a steel sheet, and does not show a clear yield phenomenon. It is difficult to increase the yield stress in proportion to the increase in tensile strength.

A weld metal having a tensile strength TS of 1200 MPa or more can be realized by increasing the hardenability by adding an alloy element to form a martensite single-phase hard structure. However, due to the formation of the martensite main structure in the weld metal, the movable dislocation density that causes the yield stress YP and the toughness vE- ₄₀ to decrease increases, and the toughness vE- ₄₀ decreases. Residual austenite is generated in the weld metal. Therefore, a conventional weld metal with a tensile strength TS of 1200 MPa or more realizes a weld metal with a yield strength YP of 1000 MPa or more and an absorbed energy vE- ₄₀ of 27 J or more in a 2 mm V notch Charpy impact test at −40 ° C. I couldn't.

In response to technical problems caused by the structure of this high-strength weld metal, the inventors have determined a predetermined amount of Ni effective for ensuring strength and toughness and other quenching elements effective for ensuring strength. In addition, one or more of Mo, W, Nb, V, and Ta, which are precipitate forming elements and ferrite forming elements, are selectively added, and the dislocation density shifts by precipitation of carbonitrides. A solid wire was developed that can improve yield strength YP and toughness vE- ₄₀ while maintaining the tensile strength TS of the weld metal while suppressing the formation of retained austenite (Patent Document 2). ,reference). The present invention also utilizes these technical ideas for designing wire components.

According to this solid wire, during gas shielded arc welding of a high-strength steel sheet, the absorbed energy vE by a 2 mmV notch Charpy impact test at −40 ° C. when the tensile strength TS is 1200 MPa or more, the yield stress YP is 1000 MPa or more. _Although it becomes possible to obtain a weld metal having _-40 of 27 J or more, there are the following problems in terms of wire productivity.

  In other words, when manufacturing a solid wire with the above composition, the strength of the material is increased due to the large amount of alloying elements contained in the material, and further, work hardening during wire drawing is added, so In the wire drawing process, the frequency of occurrence of disconnection tends to increase. For this reason, in order to perform cold wire | line drawing favorably, it is necessary to repeat the annealing process for softening a raw material, and causes a fall of wire productivity and an increase in manufacturing cost.

  In view of the problems in manufacturing a high-strength solid wire that has been designed based on the above technical idea, the present inventors have adopted a flux-cored wire and increased the hardenability element in the steel outer sheath. In the design of this wire, it is assumed that hardenable elements are contained in the flux filled in the outer shell as a metal or an alloy, thereby improving the productivity of the wire compared to the solid wire. Study was carried out.

  As a result, when a large amount of quenching element is contained in the powder state of a metal or alloy as a flux to be filled in the steel sheath of the flux-cored wire, the oxygen content as shown below is not a problem with a solid wire. In addition, it was confirmed that new problems such as a decrease in the toughness and ductility of weld metal and the occurrence of cold cracking due to an increase in hydrogen content occurred.

  That is, when manufacturing a flux-cored wire, a flux blending and granulating step not required for a solid wire is required. At this time, when a large amount of a quenching element necessary for achieving a weld metal having a tensile strength TS of 1200 MPa or more is mixed in the powder in a metal or alloy powder state, the surface of fine metal particles of the metal or alloy By forming an oxide in the metal or adsorbing with oxygen molecules or atoms in a metal or alloy powder, the oxygen content in the wire is likely to increase as compared with a solid wire.

  In addition, during the blending and granulation process of the flux, and during the storage period after manufacturing the wire, the metal or alloy powder absorbs moisture in the atmosphere, so the increase in hydrogen content in the wire is significant compared to solid wire. Become.

  The present inventors, in particular, have a weld metal with a tensile strength TS of 1200 MPa or more, and the allowable ranges of toughness and ductility are narrow, and the sensitivity to cold cracking is extremely high, so that the amount of oxygen in the weld metal increases during welding. It has been confirmed that toughness and ductility are greatly reduced, and cold cracking occurs when diffusible hydrogen increases.

  In the present invention, in response to the technical problem related to oxygen and diffusible hydrogen in the wire, the steel outer sheath of the flux-cored wire is used as a seamless pipe, and oxygen and water intrusion into the flux from the steel outer sheath is prevented. In addition to preventing, an appropriate amount of deoxidizing elements such as Si, Mn, Al, Ti, and Mg is contained in the wire, and the deoxidizing element equivalent (Aleq.) Expressed by the above formula (2) is within a predetermined range. Therefore, the technical idea is to prevent the deterioration of the toughness and ductility of the weld metal and the occurrence of cold cracking due to oxygen and diffusible hydrogen in the weld metal during welding.

  In the weld metal for high-strength steel that is the object of the present invention, the alloy element amount and hardness of the weld metal are higher than the heat-affected zone and the base material of the steel material. But not with weld metal. Therefore, the low temperature cracking susceptibility of the weld metal can be relatively compared and evaluated by the crack stop temperature in the y-type weld cracking test.

  The reason for limiting the technical requirements that characterize the flux-cored wire of the present invention will be described below.

  First, a description will be given of the components contained as a metal or alloy in the steel outer shell and the flux constituting the flux-cored wire, and the reasons for limiting the content thereof.

In addition, the content of each component shown below includes the component content in the steel sheath and the component content in the flux measured by component analysis of the steel sheath and the flux, and the filling rate of the flux (total wire Based on (mass% of the total mass of the flux with respect to the mass)), it can be obtained by the following equation (6).
Total content (% by mass) of component i in wire = content (% by mass) of component i in steel outer sheath × (1−filling rate) + content (% by mass) of component i in flux × Filling ratio (6)
In addition, the said flux total mass means the total amount of the component content in the flux containing the slag formation agent and the arc stabilizer other than the element added as a metal or an alloy. Moreover, the component content in a flux means the ratio of the element amount in the metal and alloy which contribute to a weld metal composition with respect to the flux total mass.

  Moreover, it is possible to measure the content of each of the above components by using a flux-cored wire manufacturing process and collecting from the drawn flux-cored wire and measuring by component analysis without using the above calculation method.

  In the following description, “%” means “% by mass” unless otherwise specified, and the content of each component is as described above for each component in the steel outer sheath and flux with respect to the total mass of the wire. It means the component content that is the total of the mass%.

(C: 0.08 to 0.3%)
C is an element that improves the strength, and in order to make the yield strength of the weld metal 1000 MPa or more, it is necessary to contain 0.08% or more in the welding wire.

  The higher the C content in the welding wire, the higher the C content in the weld metal, which is preferable for increasing the strength of the weld metal, but the toughness deteriorates significantly. In addition, the sensitivity of both weld metal hot cracks and cold cracks is significantly increased. In order to ensure toughness and crack resistance, the upper limit of the C content of the welding wire needs to be 0.3%.

  For these reasons, the C content in the welding wire is 0.08 to 0.3% in the present invention.

(Si: 0.2-2%)
Si is a deoxidizing element and is necessary to reduce the amount of O in the weld metal and increase the cleanliness. For that purpose, the content in the welding wire needs to be at least 0.2%. However, if the content in the welding wire exceeds 2% and becomes excessive, the toughness of the weld metal is remarkably deteriorated. Therefore, in the present invention, the Si content in the welding wire is set to 0.2 to 2%.

(Mn: 0.5-2.5%)
Mn is an essential element for ensuring hardenability and increasing strength. In order to exhibit the strength improvement effect reliably, it is necessary to make it contain 0.5% or more in a welding wire. On the other hand, if the content is 2.5% or more in the welding wire, the retained austenite is excessively generated and the yield strength does not improve relative to the content. In the present invention, the Mn content in the welding wire is limited to 0.5 to 2.5% because the possibility of weld cracking deterioration increases.

(P: 0.02% or less)
P is an impurity element and needs to be reduced as much as possible in order to inhibit toughness. However, if the content in the welding wire is 0.02% or less, an adverse effect on toughness can be tolerated. Therefore, in the present invention, P in the welding wire is acceptable. The content is 0.02% or less.

(S: 0.01% or less)
S is also an impurity element, and if it is excessively present in the weld metal, it deteriorates both toughness and ductility, so it is preferable to reduce it as much as possible. If the content in the welding wire is 0.01% or less, adverse effects on toughness and ductility can be tolerated. Therefore, in the present invention, the S content in the welding wire is 0.01% or less. In particularly high-strength weld metals with a yield strength of 1100 MPa or more, the adverse effect on ductility and toughness of S is more prominent, so the content in the welding wire should be 0.005% or less. More preferred.

(Al: 0.002-0.3%)
Al is a deoxidizing element and, like Si, is effective in reducing O and improving cleanliness in the weld metal, and is essential for keeping the O content in the weld metal within the allowable range in the flux-cored wire of the present invention. Elements. In order to exert the effect, it is necessary to contain 0.002% or more in the welding wire. On the other hand, if the content exceeds 0.3% in the welding wire, a coarse oxide is formed in the weld metal, and this coarse oxide significantly deteriorates toughness.
Therefore, in this invention, Al content in a welding wire shall be 0.002-0.3%.

(Ti: 0.005-0.3%)
Ti, like Al, is effective as a deoxidizing element, and is an essential element for keeping the amount of O in the weld metal within the allowable range in the flux-cored wire of the present invention. Furthermore, the solid solution N can be fixed to alleviate the adverse effect on the toughness of the solid solution N, and further, the heated austenite grain size can be refined in a region where TiN is formed and reheated in multi-layer welding. It is also effective in improving toughness. In order to exert these effects, it is necessary to contain 0.005% or more in the welding wire. However, if the content in the welding wire exceeds 0.3% and becomes excessive, there is a high possibility that toughness deterioration due to the formation of coarse oxides and toughness deterioration due to excessive precipitation strengthening will occur.

  For this reason, in this invention, Ti content in a welding wire shall be 0.005-0.3%.

(Ni: 0.5-11%)
Ni is the only element that can improve toughness regardless of the structure and components by solid solution toughening. In particular, Ni is an essential element for increasing toughness with a high strength weld metal having a yield strength of 1000 MPa or more. In order to reliably exhibit the solid solution toughening effect, it is necessary to contain 0.5% or more in the welding wire. The higher the Ni content, the more advantageous in improving toughness. However, if the content in the welding wire exceeds 11%, the effect is saturated, and residual austenite is generated excessively, resulting in yield strength. This is not preferable because the manufacturing cost of the welding wire becomes excessive as well as the amount is not improved. Therefore, in this invention, Ni content in a welding wire is limited to 0.5 to 11%.

(Mg: 0.012-0.5%)
Mg is a strong deoxidizing element, and is an element essential for adding in combination with Si, Mn, Al and Ti, reducing the amount of O in the weld metal, and improving the ductility and toughness of the weld metal. In order to exhibit the above, it is necessary to contain 0.012% or more in the welding wire.

  In addition, Mg can uniformly disperse fine oxides in the weld metal compared to strong deoxidation elements such as Al and Ca. Therefore, even if a relatively large amount of Mg is contained, formation of coarse oxides is possible. There is no decrease in the toughness of the weld metal due to. However, if the Mg content in the welding wire exceeds 0.5%, the reduction in toughness due to the formation of coarse oxides in the weld metal cannot be ignored, and the stability of the arc during welding deteriorates, resulting in beading. It also causes the shape to deteriorate. For this reason, in this invention, Mg content in a welding wire is limited to 0.012-0.5%.

  Further, in the present invention, in order to improve the toughness of the weld metal by utilizing the action of uniform dispersion of fine oxides by Mg, preferably, Mg is contained in an amount of 0.02 to 0.5%. It is preferable to supplementarily use other deoxidizing elements such as Ti.

  In the present invention, in addition to the above components, it is necessary to selectively add one or more of Mo, W, Nb, V, and Ta within the following content range. All of these elements have a common effect in that they are ferrite stabilizing elements and precipitation strengthening elements, and carbonitride is precipitated in the weld metal, and the movement of the mobile dislocation density in the martensite main structure is pinned. It is an extremely effective element for improving yield strength and toughness by stopping and improving toughness by suppressing the formation of retained austenite.

(Mo: 0.1 to 4%)
Mo is a hardenability improving element and is effective in reducing retained austenite because it is a ferrite stabilizing element, and is effective in securing yield strength by forming fine carbides and precipitation strengthening. In order to exert these effects, at least 0.1% is necessary even in consideration of combined effects with other elements having similar effects. On the other hand, if the content exceeds 4% in the welding wire, coarse precipitates are generated and the toughness of the weld metal is deteriorated. Therefore, in the present invention, the content when Mo is contained in the welding wire is 0. .1 to 4%.

(W: 0.1-3%)
W, like Mo, is a hardenability-improving element and is effective in reducing retained austenite because it is a ferrite-stabilizing element. Also, it forms fine carbides and ensures yield strength by precipitation strengthening. It is effective for. In order to exert these effects, at least 0.1% is necessary even in consideration of combined effects with other elements having similar effects. On the other hand, if the content exceeds 3% in the welding wire, the toughness deteriorates significantly. Therefore, in the present invention, the content in the case where W is contained in the welding wire is 0.1 to 3%.

(Nb: 0.005 to 0.1%)
Nb is also a ferrite stabilizing element, and is effective in reducing retained austenite, and is effective in securing yield strength by forming fine carbides and strengthening precipitation. In order to exert these effects, a minimum of 0.005% is necessary even in consideration of combined effects with other elements having similar effects. On the other hand, if it exceeds 0.1%, it is not preferable because it is excessively contained in the weld metal and coarse precipitates are formed to deteriorate toughness. Therefore, in the present invention, the content when Nb is contained in the welding wire is 0.005 to 0.1%.

(V: 0.005-0.5%)
V is also a ferrite stabilizing element and is effective in reducing retained austenite, and is effective in securing yield strength by forming fine carbides and strengthening precipitation. In order to exert these effects, a minimum of 0.005% is necessary even in consideration of combined effects with other elements having similar effects. On the other hand, if it exceeds 0.5%, it is not preferable because it is excessively contained in the weld metal and coarse precipitates are formed to deteriorate the toughness. Therefore, in the present invention, the content when V is contained in the welding wire is 0.005 to 0.5%.

(Ta: 0.005 to 0.5%)
Ta is also a ferrite stabilizing element, and is effective in reducing retained austenite, and is effective in securing yield strength by forming fine carbides and strengthening precipitation. In order to exert these effects, a minimum of 0.005% is necessary even in consideration of combined effects with other elements having similar effects. On the other hand, if it exceeds 0.5%, it is not preferable because it is excessively contained in the weld metal and coarse precipitates are formed to deteriorate the toughness. Therefore, in this invention, content in the case of containing Ta in a welding wire shall be 0.005-0.5%.

In the present invention, the target weld metal has tensile strength TS (1200 MPa or more), yield strength YP (1000 MPa or more), and toughness (absorbed energy vE- ₄₀ of 27 J or more in a 2 mmV notch Charpy impact test at −40 ° C.). In order to achieve the above, when the above components are added within the specified ranges of the respective contents, the carbon equivalent (Ceq.) Indicating the hardenability of the weld metal represented by the above formula (1), the above (2) Al equivalent (Aleq.) Which is an index of the deoxidation effect by the deoxidizing element represented by the formula, and Nb equivalent (Nbeq.) Which is an index of the yield stress improvement effect by the precipitate represented by the above formula (3). It is necessary to limit together.

(Carbon equivalent (Ceq.): 0.7-2%)
In the weld metal, in order to improve the tensile strength TS to 1200 MPa and yield strength to 1000 MPa or more, the hardened property of the weld metal is ensured and the transformation structure of the weld metal is basically a martensite single phase. It needs to be an organization. Although a slight bainite structure is allowed to be generated, it is necessary to make a martensite-based structure having a martensite ratio of 90% or more.

  For this purpose, the content of each element in the welding wire is limited to the above-described range, and further, the content of C, Si, Mn, Ni, Cr, Mo, and W, which are quenching components of the welding wire, is reduced. Based on this, it is necessary to set the carbon equivalent (Ceq.) As an index of hardenability represented by the above formula (2) to 0.7% or more. The larger the carbon equivalent, the more stable hardenability can be secured, but if it exceeds 2%, the increase in tensile strength will be saturated and the yield strength may decrease due to the formation of retained austenite. Moreover, since toughness deteriorates, it is not preferable.

  For the above reasons, in the present invention, the carbon equivalent (Ceq.) Of the welding wire is limited to 0.7 to 2%.

(Deoxidizing element equivalent (Aleq.): 0.2 to 0.6%)
The deoxidation element equivalent (Aleq.) Represented by the above formula (2) is an index based on experimental data in which the effect of deoxidation in the weld metal is expressed in terms of Al equivalent. In a high strength weld metal having a tensile strength of 1200 MPa or more and a yield strength of 1000 MPa or more, which is an object of the present invention, 2 mmV at −40 ° C. without deteriorating ductility and toughness due to the amount of O in the weld metal. In order to ensure a toughness of 27 J or more with the absorbed energy vE- ₄₀ in the notch Charpy impact test, it is necessary to suppress the amount of O in the weld metal below a certain level.

In FIG. : 0.8-0.85%, Nbeq. : 0.1-0.2%, Aleq. : Using a flux-cored wire having an outer diameter of 1.2 mm in the range of 0.06 to 0.96, a steel plate S2 having a plate thickness of 16 mm shown in Table 1 is heated to 1.7 kJ / mm and Ar + 20% CO ₂ . When the gas shielded arc welding is performed, the flux-cored wire Aleq. And the toughness vE- ₄₀ of the weld metal.

  The weld metal was a weld metal structure composed of a martensite main structure having a yield strength YP of 1080 to 1150 MPa.

The deoxidizing elements of Al, Mg, Ti, Si, and Mg contained in the flux-cored wire have different deoxidizing powers depending on each element, and there are also differences in the size and degree of dispersion of the oxide generated by the deoxidation. However, as shown in FIG. 1, the toughness vE- ₄₀ of the high-strength weld metal mainly composed of the martensite structure greatly affects the deoxidizing element equivalent (Aleq.) Represented by the formula (2). It can be seen that good toughness with an absorbed energy vE- ₄₀ in a 2 mmV notch Charpy impact test at −40 ° C. of 27 J or more can be stably obtained when the content is 0.2 to 0.6%. Aleq. If it is less than 0.2%, the deoxidation effect in the weld metal and the fine effect of uniform fine dispersion of the oxide cannot be sufficiently exhibited, and sufficient improvement in toughness cannot be achieved. On the other hand, Aleq. If it exceeds 0.6%, the deoxidation effect is saturated, and a coarse oxide is formed to adversely affect the toughness.

  For these reasons, when adding deoxidation elements such as Si, Mn, Al, Ti, and Mg to the wire, the present invention is within the above-described content range of each deoxidation element, and Aleq. Needs to be adjusted so as to be in the range of 0.2 to 06%.

(Nb equivalent (Nbeq.): 0.05 to 0.5%)
The effect of improving the yield strength by the precipitation elements of Mo, W, Nb, V and Ta is introduced at the time of martensitic transformation and the effect of becoming the resistance of dislocations when the carbonitride precipitated in the weld metal moves when stress is applied. This is considered to be due to the effect of precipitation on the movable dislocation and fixing the dislocation.

  With these elements, in order to make the yield strength in a martensitic single phase or weld metal consisting of a main structure having a tensile strength of 1200 MPa or more, 1000 MPa or more, the Nb equivalent represented by the above formula (3) is 0.05% or more. It is necessary to. If the Nb equivalent is less than 0.05%, the yield strength improvement effect can be sufficiently obtained even if the contents of Mo, W, Nb, V, and Ta satisfy the range defined in the present invention. Absent.

  On the other hand, if the Nb equivalent is more than 0.5%, the precipitates are coarsened and the toughness of the weld metal is greatly deteriorated.

  For these reasons, the Nb equivalent of the welding wire composition is limited to 0.05 to 0.5% in the present invention.

(Total content of slag former and arc stabilizer in the flux ≦ 20%)
When the total content of the slag forming agent and the arc stabilizer in the flux exceeds 20% by mass% with respect to the total mass of the wire, the amount of slag is excessively increased during welding, and welding workability is hindered.

  Moreover, since the slag forming agent and the arc stabilizer are metal oxides, and the amount of O in the weld metal tends to increase due to the increase in the slag forming agent and the arc stabilizer, the toughness and ductility of the weld metal are reduced. It is not preferable from the point of suppression.

  For these reasons, in the present invention, the total content of the slag forming agent and the arc stabilizer in the flux is limited to 20% or less by mass% based on the total mass of the wire.

Incidentally, the slag forming agent means TiO ₂ , SiO ₂ , ZrO ₂ , Al ₂ O ₃ , MnO, FeO, CaO, etc., which have an action of maintaining a good weld bead shape, and an arc stabilizer and Means Na ₂ O, K ₂ O, etc., which have the effect of increasing arc stability during welding, but other than this does not impede the inclusion of oxides and compounds having the same effect.

  The above is the reason for limiting the content of the basic component elements and impurities to be limited in the welding wire of the present invention, but within the range that does not hinder the basic characteristics of the weld metal intended by the present invention, For adjustment, if necessary, one or more of Cu, Cr, Co, and B can be further contained in the welding wire in the following content range.

(Cu: 0.01 to 1.5%)
Cu is inevitably contained in the wire and the weld metal when the welding wire is plated and used. Cu is an element effective for improving the strength, and in order to exert the effect, it is necessary to contain 0.01% or more. However, if it is contained excessively, deterioration of the toughness and hot cracking resistance of the weld metal is not preferable. In the present invention, the Cu content of the wire is the upper limit that does not cause deterioration of the toughness or hot cracking resistance of the weld metal, even if it is contained as plating or intentionally contained for strength improvement. The upper limit is 1.5%. Note that the content of Cu includes not only the content of the outer skin itself and the flux, but also the amount of plating on the wire surface.

(Cr: 0.01-2%)
Cr is an effective element for increasing strength by enhancing hardenability. Therefore, when it contains in a welding wire, 0.01% or more is required. On the other hand, if the content exceeds 2%, bainite and martensite are hardened unevenly and the toughness is remarkably deteriorated. Therefore, in the present invention, the upper limit of the content in the welding wire is set to 2%.

(Co: 0.01-6%)
Co is an element effective in securing the yield strength through the adjustment of the strength and the suppression of the formation of retained austenite by suppressing the extremely low transformation point in the bainite-martensite structure. In order to exhibit this effect reliably, it is necessary to make it contain 0.01% or more in a welding wire. On the other hand, if the content exceeds 6%, the effect is saturated and the manufacturing cost becomes excessive. Therefore, in the present invention, when Co is contained in the welding wire, the range is set to 0.01 to 6%.

(B: 0.001 to 0.015%)
When B is contained in an appropriate amount in the weld metal, it has the effect of reducing the adverse effect on the toughness of the solid solution N by combining with the solid solution N and contributing to the improvement of the strength by increasing the hardenability. It is an element that can. In order to exert these effects reliably, the B content in the welding wire needs to be 0.001% or more. On the other hand, when the B content in the welding wire exceeds 0.015%, the B in the weld metal becomes excessive, forming coarse B compounds such as BN and Fe23 (C, B) 6, and reverse toughness. Since it degrades, it is not preferable. Therefore, in the present invention, when B is contained in the welding wire, the content is limited to 0.001 to 0.015%.

  When the welding wire contains one or more of Cu, Cr, Co and B in addition to the basic components described above, carbon of the hardenability index represented by the above formula (4). If the equivalent Ceq is less than 0.7, the hardenability for the tensile strength TS of the weld metal image to be 1200 MPa or more cannot be sufficiently secured. If the carbon equivalent Ceq exceeds 2%, the yield stress YP and toughness are Since it deteriorates, it is not preferable. For this reason, it is preferable to limit the carbon equivalent Ceq represented by the above formula (4) to 0.7 to 2%.

  In the present invention, in addition to the above components, one or two of Ca and REM may be added to the wire within the following ranges as necessary for the purpose of adjusting the ductility and toughness of the weld metal. Can be contained.

(Ca: 0.0002 to 0.01%, REM: 0.0002 to 0.01%)
Both Ca and REM are effective in improving ductility and toughness by changing the structure of sulfides and reducing the size of sulfides and oxides in the weld metal. The lower limit content for exhibiting the effect is 0.0002%. On the other hand, excessive content causes coarsening of sulfides and oxides, leading to deterioration of ductility and toughness, and also may cause deterioration of weld bead shape and weldability. 0.01%.

  When the welding wire contains one or two of the above-mentioned Ca and REM in addition to the above-mentioned components, the deoxidizing element equivalent (Aleq.) Represented by the above formula (5) is less than 0.02. Then, the effect of improving ductility and toughness due to the reduction of the amount of O in the weld metal is reduced. On the other hand, Aleq. If it exceeds 0.6%, there is a possibility that the welding workability and the bead shape are deteriorated.

  For this reason, when 1 type or 2 types of said Ca and REM are contained, the deoxidation element equivalent (Aleq.) Shown by said Formula (5) is limited to 0.02-0.6%. Is preferred.

  In the present invention, the basic component and the selected component are contained in the steel outer shell and the flux, and when contained in the flux, the yield is lowered when added in the form of an oxide except for Mg. It is preferable to add in the form of a metal or an alloy. However, since Mg has an effect equivalent to that of a pure metal or alloy even with an oxide, it may be contained with an oxide.

  Moreover, in order to keep the density of the filling above a certain level, it is not a problem to include Fe powder for bulking as long as the chemical composition of the entire wire satisfies the present invention.

  The above is the reason for limiting the component composition of the flux-cored wire of the present invention. In the present invention, the oxygen content and hydrogen content in the wire are reduced, the weld metal is improved in toughness and ductility, and the weld metal In order to suppress cold cracking, it is necessary to make the steel outer shell constituting the flux-cored wire a seamless pipe.

  By using the steel outer shell as a seamless pipe, it is possible to suppress the intrusion of oxygen and hydrogen in the atmosphere from the steel outer shell to the flux during wire storage. In particular, moisture in the atmosphere easily enters the flux from the seam part of the outer skin, and in the outer skin where the seam part of the steel outer skin is joined by mechanical fastening such as caulking, it is not possible to prevent the entry of hydrogen sources such as moisture. This is not possible and causes cold cracking of the weld metal during welding. For these reasons, in the present invention, the steel outer shell constituting the flux-cored wire is a seamless pipe.

  The “seamless” in the present invention includes a pipe having a seam portion joined by welding such that there is no gap in the seam portion, in addition to a seamless pipe without a seam.

  In addition, the steel type of the steel outer shell is not particularly limited as long as it can maintain the wire drawability intended for the present invention and improve the productivity, and is not limited to a general steel like a mild steel with few alloying elements. Steel can be used.

  According to the above-mentioned definition of the wire component and the steel outer sheath, the flux-cored wire of the present invention can obtain a low temperature crack resistance of a weld metal equal to or higher than that of a solid wire having the same component composition.

  That is, when the flux-cored wire of the present invention is used to gas weld arc weld a 25 mm thick steel plate with a tensile strength of 950 MPa class to form a weld metal with a yield strength of 1000 MPa to 1100 MPa, a JIS Z3158y type weld crack test. It is possible to achieve low temperature crack resistance with a crack stop temperature of 100 ° C. or lower. When a flux-cored wire of the present invention is used to gas weld arc weld a 25 mm thick steel plate with a tensile strength of 1200 MPa class to form a weld metal with a yield strength of 1100 MPa to 1200 MPa, a JIS Z3158y type weld crack test. It is possible to achieve low temperature crack resistance with a crack stop temperature of 150 ° C. or lower.

(Annealing treatment)
However, for the purpose of ensuring the low temperature cracking resistant property more reliably, in order to reduce hydrogen loss in the manufacturing process, it is desired to perform cold forming from a flux cored wire having a diameter larger than the final wire diameter. In the manufacturing process of making the wire diameter, annealing at a heating temperature of 600 to 1100 ° C. can be performed at least once during or after completion of the drawing after filling the steel outer shell with the flux.

  The lower limit of the annealing temperature is set to 600 ° C. because the dehydrogenation effect is not sufficient when the temperature is lower than 600 ° C., and the upper limit is set to 1100 ° C. If the temperature exceeds 1100 ° C., unnecessary oxidation occurs in the outer skin, This is also because the amount of O as a wire is increased and the amount of O in the weld metal is increased, which may impair toughness and ductility.

  Annealing is, for example, in the state of the original wire at the stage where the flux is added into the pipe-shaped outer shell or the U-shaped outer shell material is filled with the flux and then molded into a pipe shape and the seam portion is welded. The effect does not change even in a process between cold forming dies in which the original wire is passed through the die a plurality of times to obtain the final diameter, or even when the processing is finished to the final wire diameter.

  Moreover, if annealing is performed a plurality of times at various stages, it is effective for reducing hydrogen accordingly. Further, since the steel outer shell is hardened during the cold forming, there is no particular problem in softening it to serve as a soft annealing for preparing a subsequent cold forming. It is preferable that the annealing atmosphere prevents hydrogen and oxygen from entering and oxidizing during annealing, and a vacuum or an inert gas atmosphere is preferable for the purpose.

  Moreover, it is preferable to make the temperature at the time of shaping | molding a wire into 1100 degrees C or less similarly to the upper limit of the said annealing temperature from the point which suppresses the increase in the oxygen content in a flux cored wire, More preferably, it is cold-warm. Inter-molding is desirable.

  When manufacturing the flux-cored wire of the present invention, the manufacturing conditions other than the annealing treatment conditions and the molding temperature are not restricted at all, and the effects intended by the present invention are exhibited under normal manufacturing conditions. Is possible.

The wire of the present invention can exert an effect on gas shield arc welding in general, that is, TIG, MIG, MAG, and CO ₂ welding in general. Even if the steel plate thickness is 25 mm or more and the welding heat input is 10 kJ / mm or less, the effect is not impaired even if there is dilution with the steel material, and the composition of the steel material has any tensile strength of 950 MPa or more. However, the weld metal characteristics intended by the present invention can be achieved. Further, even when the dilution from the steel material cannot be ignored due to thin heat input, the steel material composition is C: 0.06 to 0.2%, Si ≦ 1%, Mn: 0.3 to 2.5%, P ≦ 0.02%, S ≦ 0.1%, Al: 0.005 to 0.2%, Cu ≦ 1%, Ni ≦ 10%, Cr ≦ 1.5%, Mo: 0.1 to 3% , Nb ≦ 0.1%, V ≦ 0.5%, Ti ≦ 0.2%, B ≦ 0.005%, and the total of other alloy elements is 1% or less, the weld metal characteristics of the present invention There is no unacceptable adverse effect on the product.

  The flux filling rate (mass ratio of the entire filling material to the entire wire) is not particularly limited as long as the composition of the entire wire satisfies the present invention. However, from the viewpoint of ensuring the manufacturability of the wire, it is 0. .3 or less is preferable.

  The effects of the present invention will be described in more detail with reference to examples.

  Welding was performed using three types of steel plates having different chemical compositions, manufacturing methods, and plate thicknesses shown in Table 1, and wire conditions and annealing conditions in Table 4-1, and welding wires having chemical compositions in Table 4-2. We investigated weld metal properties and cold cracking resistance.

  Although all the steel plates in Table 1 have a yield strength of 1100 MPa or more, the effect of the welding wire of the present invention is not limited to the chemical composition and strength level of the steel plates in Table 1.

Welding is MAG welding in which the shielding gas is Ar + 20% CO ₂ , and a joint for evaluation of weld metal characteristics is a groove with a groove angle of 45 ° and a root gap of 7 mm. .7 kJ / mm multilayer overlay welding was used. The preheating / pass temperature was 150 ° C. The y-type weld cracking test is performed in accordance with the y-type weld cracking test method of JIS Z3158. Using a steel plate with a thickness of 25 mm, the test is performed at various preheating temperatures with a welding heat input of 1.7 kJ / mm. The stop temperature was determined. In order to take into account changes over time in the resistance to hydrogen cracking due to moisture absorption of flux-cored wires, etc., when welding is performed, welding is performed after opening the wire and storing it in the atmosphere for about 6 months. Provided. However, rust generated on the wire surface during storage was removed.

  The flux-cored wires shown in Tables 4-1 and 4-2 were manufactured by variously combining steel outer sheaths having chemical compositions shown in Table 2 and fluxes showing contents of respective elements in Table 3. A steel outer shell having a thickness of 3 mm was used, processed into a U-shape, a required amount of flux was added, and then seam welding was performed while processing the cross-section into a circular shape to obtain a seamless wire. However, as a comparative example, some of the wires may be formed by mechanical fastening by caulking. The filling rate of the flux was adjusted by a combination of the flux addition amount and the initial wire diameter. However, the Fe content was appropriately added to increase the bulk as necessary. The wire after welding was made into a final wire diameter of 1.2 mm or 1.4 mm by cold drawing. Most were annealed during and / or after cold drawing for the purpose of reducing the hydrogen source and / or softening the work-hardened wire, but some wires were not annealed for comparison. is there. Some of the wires are plated on the surface, but most are not plated with Cu. The Cu content in Table 4-2 is indicated by the total content without distinguishing whether it is contained in the flux from plating, outer skin, or flux. The flux composition in Table 3 also shows the addition ratio and type of slag former and arc stabilizer, but the slag former and arc stabilizer in the present invention have an effect on the properties of the weld metal and the hydrogen cracking characteristics. There is nothing. Therefore, the present invention is not limited to the ratio and type of the slag forming agent and arc stabilizer shown in Table 3.

  Of Tables 4-1 and 4-2, wire numbers YA1 to YA15 are flux-cored wires that satisfy the requirements of the present invention, and wire numbers YB1 to YB15 are flux-cored wires that do not satisfy the requirements of the present invention. It is.

  Table 5 shows the weld metal characteristics of the welded joint, and Table 6 shows the y-type weld crack test results together with the conditions for producing the welded joint. Tensile properties of weld metal were measured with a round bar tensile specimen taken in parallel to the weld bead longitudinal direction from the center of the weld metal in the width direction of the steel plate, and toughness was measured in the center of the thickness of the steel plate and in the center of the width of the weld metal. Evaluation was made using a standard size 2 mm V notch Charpy impact test specimen taken at right angles to the longitudinal direction of the weld bead so as to be a notch position.

  As apparent from the mechanical properties of the weld metal shown in Table 5 and / or the crack stop temperature in the y-type weld crack test shown in Table 6, the case where welding is performed using wires YA1 to YA15 satisfying the present invention. The weld metal has no weld defects such as hot cracks and cold cracks at the stage of welding, and the weld metal has a yield strength of 1000 MPa or more and a tensile strength of 1250 MPa or more. The toughness is sufficiently higher than 27J in the absorbed energy at −40 ° C. in the 2 mm V notch Charpy impact test (joint number WA1 to WA15), and the crack stop temperature in the y-type crack test is 125 ° C. or less, Compared with solid wire stopping temperature of about 150 ° C that can achieve weld metal strength level It has become a low-temperature cracking properties (Test No. WYA1~WYA15).

  On the other hand, in the case of wires with wire numbers YB1 to YB15 that do not satisfy the requirements of the present invention, at least one of wire manufacturability, joint soundness, weld metal characteristics, cold crack resistance, and the like is compared with the wire of the present invention. It is apparent that the welding wire is not preferable as a welding wire in which a structure requiring safety is welded and the yield strength of the weld metal is 1100 MPa or more.

  That is, since the wire numbers YB1 and YB2 are manufactured by caulking, the amount of diffusible hydrogen is higher than that of the present invention due to moisture absorption during storage and the like, and the stop temperature of the y-type crack test is 250 ° C. (Test symbols WYB1 and WYB2). Therefore, in the joint preheated at 150 ° C., low temperature cracking occurs after welding, and the soundness of the joint is impaired, which is not preferable.

  Since the wire number YB3 has an excessively low carbon equivalent (Ceq.), The yield strength of the weld metal does not reach 1000 MPa. Moreover, since the Al equivalent is slightly insufficient, the oxygen content in the weld metal is increased and the toughness is inferior (joint symbol WB3).

  Since the wire number YB4 does not contain any element contained in the Nb equivalent formula that increases the yield strength by precipitation strengthening in the wire, the yield strength does not reach 1000 MPa and is inferior to the present invention (joint symbol WB4). ).

  The wire number YB5 is Ceq. , Aleq. Nbeq. However, since both are below the lower limit of the present invention, the weld metal of the joint WB5 has insufficient yield strength and inferior toughness, and the difference from the present invention is clear.

  The wire number YB6 is the Ceq. First, in manufacturing a wire, since there is much deformation resistance, a wire breakage occurs during cold drawing, which is difficult to manufacture. Next, at the stage of producing the joint, both hot cracking and cold cracking occur, resulting in poor joint soundness. The toughness of the weld metal also deteriorates significantly (joint number WB6), and even in the y-type weld cracking test, the crack stop temperature exceeds the target 150 ° C and reaches 175 ° C (test number WYB7), which is not preferable.

  As for wire number YB7, Mg in the wire is excessive, and as a result, Aleq. Is too large, a coarse oxide is formed in the weld metal, and the toughness is significantly deteriorated (joint WB7).

  The wire number YB8 is the Nbeq. Is too large, wire breakage occurs during the manufacture of the wire, resulting in difficulty in manufacturability. Further, the toughness of the weld metal is also greatly deteriorated (joint number WB8), which is not preferable.

  In wire number YB9, since the Mg content of the wire is too small, the oxygen content of the weld metal is not reduced, and the toughness is significantly deteriorated (joint number WB9).

  Since wire number YB10 has an excessively low C content in the wire, Ceq. Although the present invention satisfies the present invention, both the yield strength and the tensile strength are significantly lower than those of the present invention, and the intended yield strength of ≧ 1000 MPa cannot be achieved (joint number WB10).

  The wire number YB11 is the same as Aleq. Is too small, the oxygen content of the weld metal is not reduced, and the toughness is significantly deteriorated (joint number WB11).

  The wire number YB12 is Nbeq. Is too small, the yield strength of the weld metal is lower than the tensile strength, which is less than 1000 MPa (joint number WB12).

  The wire number YB13 has a sufficiently high strength because the C content of the wire is excessive. However, since there is a large amount of deformation resistance in manufacturing the wire, wire breakage occurs during cold drawing, resulting in difficulty in manufacturability. In addition, since the toughness of the weld metal is extremely low (joint number WB13) and the low temperature cracking stop temperature is as high as 200 ° C. (test symbol WYB13), low temperature cracks are also generated in the joint preparation stage, which is not preferable.

  In the wire number YB14, since the Ni content of the wire is too small, the toughness of the weld metal is not sufficiently ensured (joint number WB14).

  The wire number YB15 is Aleq. Is within the scope of the present invention, but since the individual contents of Al and Ti are excessive, coarse oxides containing Al and Ti are formed in the weld metal, so the toughness of the weld metal is greatly deteriorated. , Not preferable (joint number WB15).

  From the above examples, according to the present invention, excellent in manufacturability and welding used for gas shielded arc welding such as MIG welding and MAG welding (Ar + CO2 welding or CO2 welding) in a high-tensile steel sheet having a tensile strength of 950 MPa or more. 150, which is similar to a solid wire with a yield strength of metal of 1000 MPa or more, an absorbed energy of 2 JV notch Charpy impact test at −40 ° C. of 27 J or more, and a cold crack stop temperature in the y-type weld crack test of the same level. It is clear that a flux-cored wire having a low temperature crack resistance equal to or lower than that of a solid wire can be obtained.

Deoxidizing element equivalent of flux-cored wire Aleq. It is a figure which shows the relationship between weld metal toughness vE- ₄₀ .

Claims (4)

In the flux-cored wire in which the flux is filled inside the steel outer sheath,
In the steel outer shell and the flux, as a metal or an alloy, in a total mass% based on the total mass of the wire,
C: 0.08 to 0.3%,
Si: 0.2-2%
Mn: 0.5 to 2.5%
P: 0.02% or less,
S: 0.01% or less,
Al: 0.002 to 0.3%,
Ti: 0.005 to 0.3%,
Ni: 0.5 to 11%,
Mg: 0.012-0.5%
And a carbon equivalent (Ceq.) Represented by the following formula (1) is 0.7 to 2%, and a deoxidizing element equivalent (Aleq.) Represented by the following formula (2) is 0.2 to 0. 6%, and
Mo: 0.1 to 4%
W: 0.1 to 3%
Nb: 0.005 to 0.1%,
V: 0.005-0.5% and
Ta: 0.005 to 0.5%
Nb equivalent (Nbeq.) Represented by the following formula (3) is 0.05 to 0.5%:
And, the total content of the slag former and arc stabilizer contained in the flux is limited to 20% or less by mass% based on the total mass of the wire, and the balance is Fe and inevitable impurities,
And the said steel outer shell is a seamless pipe, The flux cored wire for high yield strength high toughness gas shield arc welding characterized by the above-mentioned.
Ceq. = [C%] + [Mn%] / 6+ [Si%] / 24+ [Ni%] / 40+ [Mo%] / 4+ [W%] / 8 (1)
Aleq. = [Al%] + [Mg%] + [Ti%] / 10% + ([Si%] + [Mn%]) / 30 (2)
Nbeq. = [Nb%] + [V%] / 5+ [Mo%] / 20+ [W%] / 10+ [Ta%] / 5 (3)
However, the above [C%], [Mn%], [Si%], [Ni%], [Mo%], [W%], [Al%], [Mg%], [Ti%], [Nb] %], [V%], and [Ta%] are the contents of C, Mn, Si, Ni, Mo, W, Al, Mg, Ti, Nb, V, and Ta contained in the steel outer sheath and flux in the wire, respectively. The sum of mass% with respect to the total mass of the wire is shown. In the steel outer shell and flux, as a metal or alloy, and in addition to the total mass% of the total wire mass,
Cu: 0.01 to 1.5%,
Cr: 0.01-2%
Co: 0.01-6%, and
B: 0.001 to 0.015%
The high yield according to claim 1, wherein the carbon equivalent (Ceq.) Represented by the following formula (4) is 0.7 to 2%. High strength and toughness flux-cored wire for gas shielded arc welding.
Ceq. = [C%] + [Mn%] / 6+ [Si%] / 24+ [Ni%] / 40+ [Cr%] / 5+ [Mo%] / 4+ [W%] / 8 (4)
However, the above [C%], [Mn%], [Si%], [Ni%], [Cr%], [Mo%] and [W%] are contained in the steel outer sheath and flux in the wire, respectively. The total of the mass% with respect to the total mass of the wire of C, Mn, Si, Ni, Cr, Mo, and W is shown. % By mass
Ca: 0.0002 to 0.01%, and
REM: 0.0002 to 0.01%
The deoxidizing element equivalent (Aleq.) Represented by the following formula (5) is 0.2 to 0.6%. A high yield strength high toughness flux-cored wire for gas shielded arc welding as described in 1.
Aleq. = [Al%] + [Mg%] + [Ca%] + [REM%] / 5+ [Ti%] / 10% + ([Si] + [Mn]) / 30 (5)
However, the above [Al%], [Mg%], [Ca%], [REM%], [Ti], [Si], and [Mn] are Al contained in the steel outer sheath and flux in the wire, respectively. The total of the mass% with respect to the wire total mass of Mg, Ca, REM, Ti, Si, and Mn is shown.   The flux-cored wire according to any one of claims 1 to 3 is subjected to an annealing treatment at a heating temperature of 600 to 1100 ° C after filling the flux into the steel outer shell or after or after drawing. High yield strength, high toughness, flux-cored wire for gas shielded arc welding.

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